Data transmission circuit, data line driving circuit, amplifying circuit, semiconductor integrated circuit, and semiconductor memory

ABSTRACT

In a driver circuit for driving a pair of data lines, the amplitude of a differential input signal is reduced from 2.5 V to 0.6 V, which is smaller than a conventional lower-limit source voltage (approximately 1.5 V). The amplitude of the differential signal transmitted through the pair of data lines is amplified to 2.5 V by an amplifying circuit and the resulting signal is then latched by a latch circuit. After the latching by the latch circuit, the operation of the amplifying circuit is halted. The driver circuit is constituted solely by a plurality of NMOS transistors so as not to increase a leakage current flowing in the off state. Here, the threshold voltage of the NMOS transistor positioned on the ground side is reduced to a conventional lower-limit value (0.3 V to 0.6 V), while the threshold voltage of the NMOS transistor on the power-source side to a value lower than the above lower-limit value (0 V to 0.3 V), thereby enhancing a driving force of the NMOS transistor on the power-source side.

BACKGROUND OF THE INVENTION

The present invention relates to a data transmission circuit, data linedriving circuit and amplifying circuit for use in the data transmissioncircuit, and semiconductor integrated circuit and semiconductor memoryeach of which comprises the data transmission circuit.

In recent years, the capacity of a dynamic RAM (DRAM), which is amongsemiconductor integrated circuits (LSI), has been increasing at a rateof quadrupling in three years. With the increasing capacity, the chiparea of the DRAM has also multiplied 1.5-fold between every adjacentgenerations (e.g., between the 1M-bit and 4M-bit generations ). With theincreasing chip area, the wire length of signal lines for transmittingdata in the DRAM has also increased, thus inviting an increase in wiringcapacitance. Furthermore, an increase in the number of wired signallines due to a tendency of the DRAM toward a multi-bit configuration hasalso spurred the increase in wiring capacitance.

In the DRAM, charging and discharging of the signal lines accounts forthe most part of its power consumption. The above increase in wiringcapacitance in turn increases a charging and discharging current andeventually brings about an increase in the total power consumption ofthe DRAM. The increase in wiring capacity also induces an increase insignal delay.

With the increasing miniaturization of a MOS transistor element in theDRAM, a voltage-withstand ability of its oxide film has also raised aproblem.

To overcome the problem, there has been an effort to reduce an internalsource voltage in a conventional DRAM in order to improve thereliability of the oxide film as well as reduce the power consumptionand signal delay. In the conventional DRAM, a reduced voltage VINT whichwas generated inside a DRAM chip based on an external source voltage VCCis supplied to a MOS transistor circuit on the chip.

Reducing the voltage amplitude of a signal line is extremely effectivein reducing the total power consumption of an LSI: Japanese Laid-OpenPatent Publication No. 4-211515 discloses a data transmission circuitwhich operates with a small amplitude based on an internal sourcevoltage that has been reduced (reduced voltage). In the datatransmission circuit, a driver circuit composed of CMOS transistorsdrives a single data line for transmitting data with a small amplitude.A receiver circuit, as shown in FIG. 18, receives a signal having asmall amplitude from the data line and converts it to a signal having alarger amplitude.

However, the conventional data transmission circuit mentioned above isdisadvantageous in that, if a wire for transmitting data becomesconsiderably long, an input IN of the receiver circuit shown in FIG. 18changes only slowly, resulting in a lower operating speed. This isbecause the receiver circuit will not operate till the input IN thereofreaches (VCL-Vtn) or (VSL-Vtp) and that it is composed of asource-follower circuit, so that Vtn and Vtp are increased due to a bodyeffect. In addition, the conventional data transmission circuit requirestwo power supplies VCL and VSL, which causes an increase in powerconsumption accordingly.

To increase the operating speed, it is possible to compose the inputpart of the receiver circuit of an NMOS and PMOS, each having lower Vtnand Vtp. In order to reduce the threshold voltages of the MOStransistors, however, more steps and more masks are needed in theirfabrication processes. To reduce the transition time of a signalinputted to the receiver circuit, it can also be considered to provide aCMOS inverter in the upper stage of the receiver circuit, whichdisadvantageously generates a leakage current between the VCL and VSL inthe off state.

SUMMARY OF THE INVENTION

The present invention has been achieved in view of the foregoing. It istherefore an object of the present invention to implement higher-speeddata transmission consuming lower power even if a long wire isinstalled.

To attain the above object, a data transmission circuit for use in asemiconductor integrated circuit according to the present inventioncomprises, as shown in FIG. 6: a first circuit (driver circuit) 6a forconverting a first pair of differential signals, each having a firstamplitude, to a second pair of differential signals, each having asecond amplitude smaller than the above first amplitude; a pair ofsignal lines (pair of data lines) 20 for transmitting the second pair ofdifferential signals obtained through the conversion by the above firstcircuit 6a; a second circuit (amplifying circuit) 30 for converting thesecond pair of differential signals transmitted through the above pairof signal lines 20 to a third pair of differential signals, each havinga third amplitude; and a third circuit (latch circuit) 40 for latchingthe third pair of differential signals obtained through the conversionby the above second circuit 30.

With the above structure, data transmission through the pair of datalines 20 can be implemented by means of the second pair of differentialsignals, each having a voltage amplitude smaller than that of the firstpair of differential signals (pair of differential input signals).Consequently, even when the wire length of the pair of data lines 20 islarge, the influence on data transmission of the parasitic resistanceand parasitic capacitance of the pair of data lines 20 on datatransition can be suppressed as well as a charging and dischargingcurrent and signal delay can be reduced, thus realizing a semiconductorintegrated circuit which operates at a high speed and consumes lowerpower. Moreover, since a peak current can be reduced due to the reducedcharging and discharging current, the reliability and noise resistanceof signal lines can be improved. Furthermore, since the third circuit 40is provided in the lower stage of the second circuit 30, the output loadon the second circuit 30 is reduced so that the second circuit 30 can bereduced in size, thereby suppressing a current flowing from apower-source terminal to a ground terminal.

Preferably, in the above data transmission circuit, a ground line of theabove first circuit is provided independently of ground lines of othercircuits in the above semiconductor integrated circuit. With the abovestructure, a stable operation is ensured for the first circuit withoutbeing affected by a variation in the ground level due to the operationof the other circuits.

Preferably, in the above data transmission circuit, the operation of theabove second circuit is halted in synchronization with the latching ofthe above third pair of differential signals by the above third circuit.With the above structure, power consumption of the semiconductorintegrated circuit can further be reduced.

Preferably, the above data transmission circuit further comprises, asshown in FIG. 11, a fourth circuit (equalizing circuit) 60 forequalizing the potentials of the above pair of signal lines (pair ofdata lines) 20. With the above structure, the time required for apotential difference between the pair of signal lines 20 to reach aspecified value is shortened, so that data transmission is performed ata higher speed.

To attain the above object, a data line driving circuit (driver circuit)6a for differentially driving a pair of data lines 20 in a semiconductorintegrated circuit according to the present invention comprises, asshown in FIG. 6: a pair of differential input terminals 11 and 12 foraccepting a first pair of differential signals each having a firstamplitude; a pair of differential output terminals 14 and 15 connectedto the above pair of data lines 20 so as to output a second pair ofdifferential signals each having a second amplitude; a first NMOStransistor Qn11 having a gate connected to one terminal 11 of the abovepair of differential input terminals 11 and 12, a drain connected to oneterminal 14 of the above pair of differential output terminals 14 and15, and a source connected to a power source line; a second NMOStransistor Qn12 having a gate connected to the other terminal 12 of theabove pair of differential input terminals 11 and 12, a drain connectedto the drain of the above first NMOS transistor Qn11, and a sourceconnected to a ground line; a third NMOS transistor Qn13 having a gateconnected to the gate of the above second NMOS transistor Qn12, a drainconnected to the other terminal 15 of the above pair of differentialoutput terminals 14 and 15, and a source connected to the above powersource line; and a fourth NMOS transistor Qn14 having a gate connectedto the gate of the above first NMOS transistor Qn11, a drain connectedto the drain of the above third NMOS transistor Qn13, and a sourceconnected to the above ground line.

With the above structure in which the data line driving circuit 6a iscomposed of the NMOS transistors, a large voltage can be obtainedbetween the gate and source of each of the NMOS transistors Qn11 toQn14. Even when the lower-limit value of the threshold voltages of theNMOS transistors is constrained to 0.3 V to 0.6 V, a large force todrive the pair of signal lines can be obtained, so that high-speed datatransmission can be implemented with a voltage amplitude smaller than1.5 V without increasing leakage currents flowing in the off state.Moreover, the data line driving circuit 6a according to the presentinvention requires only one power source, whereas a conventional dataline driving circuit composed of CMOS transistors requires two powersources, so that power consumption of the semiconductor integratedcircuit can further be reduced. Furthermore, since the data line drivingcircuit can be composed solely of the NMOS transistors, it can befabricated easily.

Preferably, in the above data line driving circuit 6a, the thresholdvoltages of the above first and third NMOS transistors Qn11 and Qn13 arelower than the threshold voltages of the above second and fourth NMOStransistors Qn12 and Qn14. With the above structure, even when thethreshold voltages of the first and third NMOS transistors Qn11 and Qn13positioned on the power-source side are set to a value lower than aconventional lower-limit value (approximately 0.3 to 0.6 V), leakagecurrents flowing through the Qn11 and Qn13 in the off state areprevented by the second and fourth NMOS transistors Qn12 and Qn14positioned on the ground side. Consequently, by setting the thresholdvoltages of the Qn11 and Qn13 lower than the threshold voltages of theQn12 and Qn14, the driving forces of the Qn11 and Qn13 can further beenhanced without increasing the leakage currents flowing in the offstate.

To attain the above object, an amplifying circuit for amplifying a pairof differential signals inside a semiconductor integrated circuitaccording to the present invention comprises, as shown in FIG. 17: apair of differential input terminals 31 and 32 for accepting the abovepair of differential signals; an amplifier 36 for amplifying the pair ofdifferential signals inputted via the above pair of differential inputterminals 31 and 32; a pair of differential output terminals 34 and 35for outputting the pair of differential signals which have beenamplified by the above amplifier 36; and a power source controller 37for controlling power supply to the above amplifier 36 based on outputsfrom the above pair of differential output terminals 34 and 35.

With the above structure, power supply to the above amplifier 36 iscontrolled based not on the pair of differential input signals, eachhaving the smaller amplitude, but on the pair of differential outputsignals which have been amplified by the amplifier 36. Consequently, theoperation of the amplifier 36 can surely be halted, thereby furtherreducing the power consumption of the semiconductor integrated circuit.

Preferably, in the above amplifying circuit, the above power sourcecontroller 37 comprises, as shown in FIG. 17, first and second PMOStransistors Qp37 and Qp38 which are connected in series to each otherand which are interposed between a power source line and the aboveamplifier 36, wherein the above first PMOS transistor Qp37 has its gateconnected to one terminal 35 of the above pair of differential outputterminals 34 and 35, and the above second PMOS transistor Qp38 has itsgate connected to the other terminal 34 of the above pair ofdifferential output terminals 34 and 35. With the above structure, sinceoutputs are the pair of differential signals, at least either of thefirst and second PMOS transistors Qp37 and Qp38 constituting the powersource controller 37 is surely turned off.

To attain the above object, a semiconductor integrated circuit accordingto the present invention comprises, as shown in FIG. 9: a main sourcewiring system 56 and a subordinate source wiring system 57, each havinga power source line and a ground line; a first circuit block 51connected directly to the above main source wiring system 56; a secondcircuit block 52 connected directly to the above subordinate sourcewiring system 57; and a source-system coupled circuit 70 interposedbetween the above main source wiring system 56 and subordinate sourcewiring system 57 so as to prevent noise propagation from the above firstcircuit block 51 to the above second circuit block 52.

With the above structure, the source-system coupled circuit 70interposed between the main source wiring system 56 and subordinatesource wiring system 57 suppresses the noise propagation from the firstcircuit block 51 to the second circuit block 52.

Preferably, in the above semiconductor integrated circuit, the abovesource-system coupled circuit 70 comprises, as shown in FIG. 9, firstand second NMOS transistors Qn71 and Qn72 which are connected inparallel to each other and which are interposed between the ground lineof the above main source wiring system 56 and the ground line of theabove subordinate source wiring system 57, the above first NMOStransistor Qn71 has its gate supplied with a control clock, and theabove second NMOS transistor Qn72 has its gate connected to the groundline of the above subordinate source wiring system 57. With the abovestructure, if the first NMOS transistor Qn71, which is one of the twoNMOS transistors Qn71 and Qn72 constituting the source-system coupledcircuit 70, is turned on in response to the control clock, the groundline 56 for the main source wiring system is connected to the groundline 57 for the subordinate source wiring system with a low impedance.While the first NMOS transistor Qn71 is in the off state, the secondNMOS transistor Qn72 functions as a MOS diode for preventing the noisepropagation from the ground line 56 for the main source wiring system tothe ground line 57 for the subordinate source wiring system.Consequently, even when the second circuit block 52 has a driver circuitwhich handles the above pair of differential signals, each having thesmaller voltage amplitude, the malfunction thereof can be prevented.

To attain the above object, a first semiconductor memory according tothe present invention comprises, as shown in FIG. 1 or FIG. 2: a dataprocessing unit 3 and at least one memory unit 2 disposed on a singlesemiconductor chip 1; and a pad 4 disposed on the above semiconductorchip 1 so as to perform at least either of the inputting of a signalfrom the outside of the semiconductor chip 1 or the outputting of asignal to the outside thereof, the above pad 4 being disposed betweenthat portion of the above semiconductor chip 1 in which the above memoryunit 2 is disposed and that portion of the above semiconductor chip 1 inwhich the above data processing unit 3 is disposed.

With the above structure, since the memory unit 2 and data processingunit 3 are provided on the same semiconductor chip 1, a conventionaldata exchange between a memory chip and a data processing chip becomesno more necessary, so that the data transmission speed can be increasedeasily, thus providing a data processing system that is simple anddensely packed. Moreover, since it is no more necessary to provide adata bus for connecting the memory chip to the data processing chip onthe board, a current for driving the data bus on the board can be saved,thereby reducing power consumption of the data processing system. Inaddition, since the pad 4 is disposed at precisely the midpoint betweenthe memory unit 2 and data processing unit 3, the lengths of wiresconnecting the pad 4 to the memory unit 2 and connecting the pad 4 tothe data processing unit 3 can be reduced. As a result, a delay in theoperating speed can be prevented. Furthermore, since a wired region canbe reduced, an increase in chip area can be prevented and an inputcapacitance of a signal line terminal viewed from the outside can alsobe reduced. Consequently, a simple data processing system which allowshigh-speed processing can be constituted and an optimum layout in asemiconductor chip can be achieved.

Preferably, in the above first semiconductor memory provided with aplurality of memory units 2, as shown in FIG. 1, the above dataprocessing unit 3 is disposed in the central portion of the abovesemiconductor chip 1, the above plurality of memory units 2 are disposedin the marginal portion of the above semiconductor chip 1, and the abovepad 4 is disposed in the intermediate portion positioned between thecentral portion and marginal portion of the above semiconductor chip 1.With the above structure, the data processing unit 3 is disposed in thecentral portion of the semiconductor chip 1 and the plurality of memoryunits 2 are disposed in the marginal portion of the semiconductor chip1, so that the lengths of wires connecting the memory units 2 to thedata processing unit 3 are equal. Consequently, and undesired reductionin the operating speed which results from the access of the processingunit 3 to a specific memory unit 2 can be prevented.

To attain the above object, a second semiconductor memory according tothe present invention comprises, as shown in FIG. 3(a) and 3(b): amemory array 122 and data processing unit 3 disposed on a singlesemiconductor chip 1; a source voltage terminal (source voltage pad) 125disposed on the above semiconductor chip 1 so as to supply a sourcevoltage to the above memory array 122 and data processing unit 3; aground voltage terminal (ground voltage pad) 126 disposed on the abovesemiconductor chip 1 so as to supply a ground voltage to the abovememory array 122 and data processing unit 3; a memory array supplyvoltage generating circuit (reference voltage generating circuit) 127disposed on the above semiconductor chip 1 so as to receive the sourcevoltage from the above source voltage terminal 125 and the groundvoltage from the above ground voltage terminal 126 and generate a memoryarray supply voltage to be supplied to the above memory array 122; and ameans for cutting off a current (switching element) 129 disposed on theabove semiconductor chip 1 so as to cut off a current flowing from theabove source voltage terminal 125 through the above memory array supplyvoltage generating circuit 127 to the above ground voltage terminal 126.

With the above structure, in the case of inspecting a source currentflowing through the data processing unit 3 on standby, a current flowingfrom the source voltage terminal 125 through the memory array supplyvoltage generating circuit 127 to the ground voltage terminal 126 can becut off by the means for cutting off a current 129, so that a sourcecurrent failure during standby can be detected in the data processingunit 3. Consequently, a simple data processing system which allowshigh-speed data processing can be constituted as well as an effectiveinspection can be executed with respect to a source current duringstandby.

To attain the above object, a third semiconductor memory according tothe present invention comprises, as shown in FIGS. 5(a) and 5(b): amemory array 122 and data processing unit 3 disposed on a singlesemiconductor chip 1; a first source voltage terminal (first sourcevoltage pad) 125a disposed on the above semiconductor chip 1 so as tosupply a source voltage to the above memory array 122; a second sourcevoltage terminal (second source voltage pad) 125b disposed on the abovesemiconductor chip 1 so as to supply the source voltage to the abovedata processing unit 3; and a memory array supply voltage generatingcircuit (reference voltage generating circuit) 127 disposed on the abovesemiconductor chip 1 so as to receive the source voltage from the abovefirst source voltage terminal 125a and generate a memory array supplyvoltage to be supplied to the above memory array 122.

In the above structure, there are provided: the first source voltageterminal 125a for supplying the source voltage to the memory array 122and memory array supply voltage generating circuit 127; and the secondsource voltage terminal 125b for supplying the source voltage to thedata processing unit 3. As a result, a current flows from the firstsource voltage terminal 125a into the memory array supply voltagegenerating circuit 127 and does not affect a current flowing from thesecond source voltage terminal 125b into the data processing unit 3. Inthe case of inspecting a source current during standby, therefore, themeasurement of the source current flowing through the memory array 122on standby can be performed independently of the measurement of thesource current flowing through the data processing unit 3 on standby, sothat it is also possible to detect a source current failure in the dataprocessing unit 3 on standby. Moreover, since the control signal forcontrolling the means for cutting off a current (switching element),which was required in the above second semiconductor memory), is notrequired, control over the chip can be simplified. Consequently, asimple data processing system which allows high-speed data processingcan be constituted as well as an effective inspection can be executedwith respect to a source current during standby.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a layout diagram showing an example of a DRAM according to afirst embodiment of the present invention;

FIG. 2 shows another layout diagram showing another example of the DRAMin which the components are placed differently;

FIG. 3(a) is a block diagram showing an example of circuit for supplyinga specified voltage to a memory array and data processing unit in theDRAM of the first embodiment;

FIG. 3(b) is a block diagram showing the structure of a voltageconverting circuit in the circuit of FIG. 3(a);

FIG. 4 is a circuit diagram showing the structure of a reference voltagegenerating circuit in the voltage converting circuit of FIG. 3(b);

FIG. 5(a) is a block diagram showing another example of the circuit forsupplying a specified voltage to the memory array and data processingunit in the DRAM of the first embodiment;

FIG. 5(b) is a block diagram showing the structure of the voltageconverting circuit in the circuit of FIG. 5(a);

FIG. 6 is a circuit diagram showing the structure of a data transmissioncircuit in the DRAM of the first embodiment;

FIGS. 7(a) to (g) are timing charts showing the operation of the datatransmission circuit according to the first embodiment;

FIG. 8 is a wiring diagram showing an example of a ground line in theDRAM of the first embodiment;

FIG. 9 is a wiring diagram showing another example of the ground line inthe DRAM of the first embodiment;

FIG. 10 is a circuit diagram showing the structure of a source voltagereducing circuit;

FIG. 11 is a circuit diagram showing part of the data transmissioncircuit of the DRAM according to the second embodiment.

FIGS. 12(a) to 12(h) are timing charts showing the operation of the datatransmission circuit according to a second embodiment;

FIG. 13(a) is a circuit diagram showing a circuit to be subjected to asimulation in the data transmission circuit of a conventional DRAM;

FIG. 13(b) is a circuit diagram showing a circuit to be subjected to asimulation in the data transmission circuit according to the firstembodiment;

FIG. 13(c) is a circuit diagram showing a circuit to be subjected to asimulation in the data transmission circuit according to the secondembodiment;

FIGS. 14(a) to (d) are timing charts showing conditions for a simulationin the circuits of FIGS. 13(a) to 13(c);

FIG. 15 is a view showing the results of a simulation on the powerconsumption of the circuits of FIGS. 13(a) to 13(c);

FIG. 16 is a view showing the results of a simulation on the powerconsumption of the circuits of FIGS. 13(a) to 13(c);

FIG. 17 is a circuit diagram showing the structure of an amplifyingcircuit for use in the data transmission circuit of the DRAM accordingto the third embodiment; and

FIG. 18 is a circuit diagram showing the structure of a receiver circuitin a conventional data transmission circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

Below, a first embodiment of the present invention will be describedwith reference to the drawings.

FIG. 1 is a view showing a DRAM according to the first embodiment, inwhich eight memory units 2 and a data processing unit 3 are provided ona semiconductor chip 1. The data processing unit 3 is disposed in thecentral portion of the semiconductor chip 1, while the eight memoryunits 2 are disposed in the marginal portion of the semiconductor chip 1so as to surround the data processing unit 3. In the intermediateportion between the central portion and marginal portion of thesemiconductor chip 1 are disposed a plurality of input pads 4 foraccepting an external signal. The intermediate portion also serves as awired region in which wires for interconnecting the memory units 2, dataprocessing unit 3, and input pads 4 (the drawing thereof is omitted withsome exceptional parts).

In the DRAM in which the memory units 2, data processing unit 3, andinput pads 4 are disposed on the semiconductor chip 1, the operationbetween the memory units 2 and data processing unit 3 is free from anundesired speed reduction resulting from the access of the dataprocessing unit 3 to a specified memory unit 2, since the distancesbetween the individual memory units 2 and the data processing unit 3 onthe semiconductor chip 1 are the same. The operation between the memoryunits 2 or data processing unit 3 and the outside of the semiconductorchip 1 is also free from a speed reduction, since the input pads 4 arepositioned precisely at the midpoints between the memory units 2 anddata processing unit 3 and hence it is possible to reduce the length ofa wire connecting the input pad 4 to the memory unit 2 and the length ofa wire connecting the input pad 4 to the data processing unit 3.Moreover, since the wired region can be reduced, an increase in chiparea and the input capacitance of a signal line terminal viewed from theoutside of the semiconductor chip 1 can also be reduced advantageously.

Each of the memory units 2 comprises: a memory core 5 including a memoryarray, decoder circuit, control circuit, and the like; an I/O block 6;and a voltage conversion circuit 7 for generating an internal sourcevoltage to be used inside the memory unit 2. The I/O block 6 has a datatransfer element 6c for executing bilateral data transfer between thememory unit 2 and data processing unit 3 via a data bus 10. The datatransfer element 6c consists of: a driver circuit 6a for sending data tothe data bus 10 so that the data is transferred to the data processingunit 3; and a receiver circuit 6b for receiving from the data bus 10 thedata sent from the data processing unit 3.

The data processing unit 3 comprises: a data processing block 8 forperforming intrinsic data processing; and an I/O block 9 having a datatransfer element 9c which consists of a driver circuit 9a and a receivercircuit 9b, similarly to the memory unit 2.

In the present embodiment, although data transfer is performed onlybetween the data processing unit 3 and each of the memory units 2, it ispossible to exchange data between the memory units 2. It is alsopossible to constitute the pad 4 so that it not only accepts an externalsignal but also outputs a signal generated inside the DRAM to theoutside.

FIG. 2 is a view showing another example of the layout of the componentsof the DRAM. A description of the same components as shown in FIG. 1 isomitted here by providing the same reference numerals. As shown in FIG.2, it is possible to provide the memory unit 2 and data processing unit3 on the same semiconductor chip 1 so that the memory unit 2 is disposedon one portion of the semiconductor chip 1 (on the right of FIG. 2),while the data processing unit 3 is disposed on the other portionthereof (on the left of FIG. 2), with a plurality of input pads 4aligned in the central portion of the semiconductor chip 1 lying betweenthe portion in which the memory unit 2 is disposed and the portion inwhich the data processing unit 3 is disposed. In the case where aplurality of memory units 2 are used, they are aligned on one portion(e.g., on the right of FIG. 2) of the semiconductor chip 1.

FIG. 3(a) exclusively shows one memory unit 2, the data processing unit3, and a circuit for supplying a specified voltage to these componentfrom the outside, which are provided in the DRAM of the presentembodiment shown in FIG. 1.

In FIG. 3(a), a memory array 122 constituting the memory core of thememory unit 2 and the data processing unit 3 are provided on the samesemiconductor chip 1. On the semiconductor chip 1 are also provided: thevoltage conversion circuit 7; a source voltage pad 125 for supplying asource voltage VDD to the memory array 122 and data processing unit 3;and a ground voltage pad 126 for supplying a ground voltage VSS to thememory array 122 and data processing unit 3. The voltage conversioncircuit 7 receives the source voltage VDD from the source voltage pad125 and the ground voltage VSS from the ground voltage pad 126 andgenerates, e.g., a reference voltage or a 1/2 source voltage.

FIG. 3(b) is a block diagram showing the structure of the voltageconversion circuit 7. As shown in FIG. 3(b), the voltage conversioncircuit 7 consists of: a reference voltage generating circuit 127serving as a memory array supply voltage generating circuit; a drivingcircuit 128; and a switching element 129 serving as a means for cuttingoff a current which is brought into the non-conducting state byactivating a test control signal TCS. As shown in FIG. 4, the simplestembodiment of the reference voltage generating circuit 127 is composedof a resistance 130. FIG. 4 shows a circuit in an ordinary state inwhich the switching element 129 is conducting. In this case, a currentis allowed to flow from the source voltage pad 125 through theresistance 130 to the ground voltage pad 126, thereby dividing thesource voltage VDD and generating a voltage VDD/2 at an output node 131.

In a DRAM in which the memory array and data processing unit are mountedtogether, a current flowing from the source voltage pad 125 through thereference voltage generating circuit 127 to the ground voltage pad 126in inspecting a source current during standby is larger than a sourcecurrent flowing through the data processing unit 3 on standby by two tothree orders of magnitude. Consequently, a source current failure in thedata processing unit 3 on standby is disadvantageously hidden by thesource current flowing through the memory array 122 on standby.

In the present embodiment, however, the switching elements 129 areinterposed between the source voltage pad 125 and the reference voltagegenerating circuit 127 of the voltage conversion circuit 7 and betweenthe ground voltage pad 126 and the reference voltage generating circuit127 of the voltage conversion circuit 7, so as to overcome the abovedisadvantage.

In the case of inspecting the source current flowing through the memoryarray 122 on standby, the test control signal TCS is inactivated so asto measure the current with the switching elements 129 in the conductingstate.

In the case of inspecting the source current flowing through the dataprocessing unit 3 on standby, on the other hand, the test control signalTCS is activated so as to measure the current with the switchingelements 129 in the non-conducting state. As a result, since the currentis not allowed to flow from the source voltage pad 125 to the groundvoltage pad 126, a source current failure in the data processing unit 3on standby can be detected.

Although the switching elements 129 are provided between the sourcevoltage pad 125 and the reference voltage generating circuit 127 of thevoltage conversion circuit 7 and between the ground voltage pad 126 andthe reference voltage generating circuit 127 of the voltage conversioncircuit 7, a similar effect can be obtained if either of the switchingelements 129 is solely provided.

FIG. 5(a) shows another example of the circuit for supplying a specifiedvoltage to the memory array 122 of the memory unit 2 and to the dataprocessing unit 3.

In FIG. 5(a), the memory array 122 constituting the memory core of thememory unit 2 and the data processing unit 3 are provided on the samesemiconductor chip 1. On the semiconductor chip 1 are also provided: thevoltage conversion circuit 7a; a first source voltage pad 125a forsupplying the source voltage VDD to the memory array 122; a first groundvoltage pad 126a for supplying the ground voltage VSS to the memoryarray 122; a second source voltage pad 125b for supplying the sourcevoltage VDD to the data processing unit 3; and a second ground voltagepad 126b for supplying the ground voltage VSS to the data processingunit 3. The voltage conversion circuit 7a receives the source voltageVDD and the ground voltage VSS from the first source voltage pad 125aand from the first ground voltage pad 126a, respectively, and generates,e.g., the reference voltage and 1/2 source voltage.

FIG. 5(b) is a block diagram showing the structure of the voltageconversion circuit 7a. As shown in FIG. 5(b), the voltage conversioncircuit 7a consists of: the reference voltage generating circuit 127serving as the memory array supply voltage generating circuit; and thedriving circuit 128. The reference voltage generating circuit 127 usedhere is the same as the reference voltage generating circuit shown inFIG. 4.

In the present embodiment, the first source voltage pad 125a connectedto the memory array 122 and to the voltage conversion circuit 7a isphysically separated from the second source voltage pad 125b connectedto the data processing unit 3, while the first ground voltage pad 126aconnected to the memory array 122 and to the voltage conversion circuit7a is physically separated from the second ground voltage pad 126bconnected to the data processing unit 3. Consequently, a current isallowed to flow from the first source voltage pad 125a through thereference voltage generating circuit 127 to the first ground voltage pad126a and does not affect a current flowing from the second sourcevoltage pad 125b through the data processing unit 3 to the second groundvoltage pad 126b. As a result, in the case of inspecting the sourcecurrents during standby, the source current flowing through the memoryarray 122 on standby can be measured independently of the measurement ofthe source current flowing through the data processing unit 3 onstandby, so that a source current failure flowing through the dataprocessing unit 3 on standby can also be detected.

According to the present embodiment, since the test control signal forcontrolling the switching elements as the means for cutting off acurrent is no more necessary, control over the chip can be simplified.

FIG. 6 exclusively shows the structure of the data transmission circuitprovided in the DRAM of the first embodiment shown in FIG. 1. Here, adescription will be given to a unilateral data transmission circuitconsisting of: the driver circuit 6a in the memory unit 2; the receivercircuit 9a in the data processing unit 3; and a pair of data linesconnecting the above two circuits. As for a data transmission circuitconsisting of: the driver circuit 9a in the data processing unit 3; thereceiver circuit 6b in the memory unit 2; and a pair of data linesconnecting these circuits, it is similar to the data transmissioncircuit mentioned above. The data bus 10 shown in FIG. 1 is composed ofthe above two pairs of data lines.

In FIG. 6, a reference numeral 6a designates a driver circuit (data linedriving circuit) of the memory unit 2, 20 designates a pair of datalines, 30 designates an amplifying circuit, and 40 designates a latchcircuit. The amplifying circuit 30 and latch circuit 40 constitute thereceiver circuit 9b of the data processing unit 3. Here, VINT designatesa first reduced voltage and VINTL designates a second reduced voltage,which is lower than the first reduced voltage VINT. Each of the VINT andVINTL is generated from an external source voltage VCC by voltagereducing circuits (not shown). For example, VCC=3.3 V, VINT=2.5 V, andVINTL=0.6 V.

The driver circuit 6a is for differentially driving the pair of datalines 20 by converting a pair of differential input signals IN/XIN,which swing between 0 V and VINT, to a pair of differential signals,each having a smaller amplitude, which swing between 0 V and VINTL. Thedriver circuit 6a comprises: a pair of differential input terminals 11and 12 for accepting the IN/XIN; a control terminal 13 for accepting afirst control signal CONT1; a pair of differential output terminals 14and 15 connected to the pair of data lines 20; and first to sixth NMOStransistors Qn11 to Qn16. The Qn11 has its gate connected to thedifferential input terminal 11, which is one of the pair of differentialinput terminals 11 and 12, has its drain connected to the differentialoutput terminal 14, which is one of the pair of differential outputterminals 14 and 15, and its source connected to the VINTL via the Qn15.The Qn12 has its gate connected to the other differential input terminal12, has its drain connected to the terminal 14, similarly to the drainof the Qn11, and its source connected to a ground line (ground level: 0V) via the Qn16. The Qn13 has its gate connected to the terminal 12,similarly to the gate of the Qn12, has its drain connected to the otherdifferential output terminal 15, and its source connected to the VINTLvia the Qn15, similarly to the source of the Qn11. The Qn14 has its gateconnected to the terminal 11, similarly to the gate of the Qn11, itsdrain connected to the terminal 15, similarly to the drain of the Qn13,and its source connected to the ground line via the Qn16, similarly tothe source of the Qn12. The gates of the Qn15 and Qn16 are connected incommon to the control terminal 13. Each of the threshold voltages of theQn11 to Qn14 is about 0.5 V.

The pair of data lines 20 are for transmitting the pair of differentialsignals, each having a smaller amplitude, which were outputted from thedriver circuit 6a to the amplifying circuit 30 and each data line has: aresistive component RL; and a capacitive component CL as distributedconstants.

The amplifying circuit 30 is for amplifying a pair of differentialsignals OUT/XOUT, which have been transmitted through the pair of datalines 20 and which swing between 0 V and VINTL, to a pair ofdifferential signals AOT/XAOT which swing between 0 V and VINT. Theamplifying circuit 30 comprises: a pair of differential input terminals31 and 32 for accepting the OUT/XOUT; a control terminal 33 foraccepting a second control signal CONT2; a pair of differential outputterminals 34 and 35 connected to the latch circuit 40; first to sixthPMOS transistors Qp31 to Qp36; and first to tenth NMOS transistors Qn31to Qn3a.

The latch circuit 40 is for latching the AOT/XAOT from the amplifyingcircuit 30 and obtaining a pair of differential output signals BOT/XBOTwhich swing between 0 V and VINT. The latch circuit 40 comprises: a pairof differential input terminals 41 and 42 for accepting the AOT/XAOT; acontrol terminal 43 for accepting a third control signal CONT3; a pairof differential output terminals 44 and 45 for outputting the BOT/XBOT;first and second PMOS transistors Qp41 and Qp42; and first to sixth NOMStransistors Qn41 to Qn46.

FIGS. 7(a) to 7(g) are timing charts showing the operation of the datatransmission circuit of FIG. 6. When the CONT1 is raised to the HIGHlevel, a data transmission cycle is initiated. In each cycle, the IN/XINhaving the amplitude VINT is converted by the driver circuit 6a to theOUT/XOUT having the smaller amplitude VINTL, which is then amplified bythe amplifying circuit 30 to the AOT/XAOT having the amplitude VINT. Atthis point, the CONT3 is raised to the HIGH level and the AOT/XAOT islatched by the latch circuit 40, so that the BOT/XBOT are determined.Then, the CONT2 is raised to the HIGH level after the determination ofthe BOT/XBOT, so that the operation of the amplifying circuit 30 ishalted in synchronization with the latching of the AOT/XAOT by the latchcircuit 40.

As described above, since the voltage amplitude of the pair of datalines 20 is limited to the VINTL, a current for charging and dischargingthe pair of data lines 20 can be reduced according to the presentembodiment. The present embodiment is particularly effective in the casewhere a ratio of the wiring capacitance of the pair of data lines 20 tothe overall capacitance of the data transmission circuit iscomparatively large. Moreover, in the driver circuit 6a composed solelyof the NMOS transistors, each of the gates of the Qn11 to Qn14 acceptsthe IN/XIN which swing between 0 V and VINT, while the magnitude of avoltage applied between the source and drain of each of the Qn11 to Qn14is limited to the VINTL. Consequently, if the magnitude of a differencebetween the VINT and VINTL is sufficient to ensure a sufficiently largegate-source voltage in each of the Qn11 to Qn14, the driver circuit 6aoperates at a high speed. Even if the lower limit of the thresholdvoltages of the Qn11 to Qn14 is constrained to 0.3 V to 0.6 V, a largeforce to drive the pair of data lines 20 can be obtained, so thathigh-speed data transmission can be implemented with a voltage amplitudesmaller than 1.5 V without increasing a leakage current flowing in theoff state.

In the amplifying circuit 30 according to the present embodiment, sincethe signals OUT/XOUT from the differential input terminals 31 and 32 areinputted to the gates of the Qp31 to Qp34, there should be no problem ifthe signals make slow transitions. However, since the amplitude of theOUT/XOUT is limited to the magnitude of the VINTL, a current willconstantly flow from the VINT through the Qp31 to Qp34 to the groundline. However, since the CONT 2 is given to the amplifying circuit 30 soas to halt the operation of the amplifying circuit 30 in synchronizationwith the latching of the AOT/XAOT by the latch circuit 40, as describedabove, the Qp35 and Qp36 prevent the current from flowing. Moreover,since the latch circuit 40 is provided in the lower stage of theamplifying circuit 30, the output load on the amplifying circuit 30becomes smaller and therefore the MOS transistors constituting theamplifier 30 can be reduced in size, so that the current flowing fromthe power source to the ground can be suppressed even when the Qp35 andQp36 are in the on state.

It is possible to arrange the present embodiment so that the VCC isapplied as it is to an intended portion of the VINT generated from theVCC. The HIGH levels of the IN/XIN, AOT/XAOT, and BOT/XBOT arepreferably in the range of 1 V to 3.3 V. The HIGH level of the OUT/XOUTis preferably in the range of 0.1 V to 1.5 V.

In the driver circuit 6a, it is possible to set the threshold voltagesof the Qn11 and Qn13 positioned on the power-source side at values lowerthan the values of the threshold voltages of the Qn12 and Qn14 on theground side. Specifically, the threshold voltages of the Qn11 and Qn13are set to 0 V to 0.3 V, while setting threshold voltages of the Qn12and Qn14 are set to 0.3 V to 0.6 V. Thus, even when the thresholdvoltages of the Qn11 and Qn13 are set to a value lower than theconventional lower limit (0.3 V to 0.6 V), if the data transmissioncircuit is controlled so that the potentials of the differential inputterminals 11 and 12 become 0 V during standby, leakage currents areprevented to flow through the Qn11 and Qn13 in the off state. Therefore,by setting the threshold voltages of the Qn11 and Qn13 lower than thethreshold voltages of the Qn12 and Qn14, the driving forces of the Qn11and Qn13 can further be enhanced without increasing the leakage currentflowing in the off state. The gate-source voltages of the Qn11 and Qn13inevitably become smaller than those of the Qn12 and Qn14, so that thelowering of the threshold voltages of the Qn11 and Qn13 is effective inenhancing the driving force of the driver circuit 6a.

FIG. 8 is a wiring diagram showing noise control over the ground line inthe DRAM of the first embodiment. The noise control was achieved in viewof the fact that the driver circuit 6a handles the pair of differentialsignals, each having the smaller amplitude, which swing between 0 V andVINTL.

In FIG. 8, a reference numeral 51 designates a first circuit blockoperating with the standard amplitude VINT, which includes, in additionto the amplifying circuit 30 and latch circuit 40 of the receivercircuit 9b, a timing generator and decoder circuit, and the likeprovided in the DRAM. A reference numeral 52 designates a second circuitblock operating with the smaller amplitude VINTL. The driver circuit 6acorresponds to the second circuit block. The first circuit block 51 isconnected to a ground pad 55 via a ground line 53, while the secondcircuit block 52 is connected to a ground pad 55 via a ground line 54provided independently of the ground line 53 of the first circuit block51. Here, if it is assumed that an extremely large current is allowed toflow through the ground line 53 due to the operation of the circuits inthe first circuit block 51, a voltage reduction is caused by a resistivecomponent RL1 of the ground line 53, so that the ground level of thefirst circuit block 51 varies to a large extent. However, since theground line 54 is provided independently of the ground line 53 in thefirst circuit block 51, the driver circuit 6a in the second circuitblock 52 is seldom affected by the variation in the ground level of thefirst circuit block 51 and can continue a proper operation. A referencenumeral RL2 designates a resistive component of the ground line 54.

Thus, by adopting the ground wiring as shown in FIG. 8, the intrusion ofpower-source noise resulting from an operating current in the firstcircuit block 51 into the second circuit block 52 can be suppressed to acertain extent.

FIG. 9 is a wiring diagram showing another example of the noise controlover a ground line. The wiring of the ground line of FIG. 9 was alsoinstalled under the noise control in view of the fact that the drivercircuit 6a handles the pair of differential signals, each having thesmaller amplitude, similarly to the case shown in FIG. 8. The first andsecond circuit blocks 51 and 52 shown in FIG. 9 are the same as thoseshown in FIG. 8. The ground line is divided into a first ground line 56for the first circuit block 51 (ground line of main source wiringsystem) and a second ground line 57 for the second circuit block 52(ground line of subordinate source wiring system). The first ground line56 is connected to the ground pad 55, while the second ground line 57 isconnected to the first ground line 56 via a source-system coupledcircuit 70. A reference numeral 80 designates a source voltage reducingcircuit for supplying the VINTL to the second circuit block 52.

The source-system coupled circuit 70 is for coupling the first groundline 56 to the second ground line 57 so as to prevent the noisepropagation from the first circuit block 51 to the second circuit block52. The source-system coupled circuit 70 comprises first and second NMOStransistors Qn71 and Qn72 connected in parallel to each other. The gateof the Qn71 is supplied with a control clock via a control terminal 71.On the other hand, the gate of the Qn72 is connected to the secondground line 57 so that the Qn72 functions as a MOS diode.

Of the two NMOS transistors constituting the source-system coupledcircuit 70, the Qn71 connects the first ground line 56 to the secondground line 57 with a low impedance if it is turned on by the controlclock supplied via the control terminal 71 during the standby of theDRAM. During the operation of the DRAM, i.e., while the Qn71 is in theoff state, the Qn72 functions as a MOS diode so as not to transmit, tothe second ground line 57, the raised level of the ground voltage in thefirst ground line 56 which accompanies the operation of the firstcircuit block 51.

As described above, the driver circuit 6a handles the pair ofdifferential signals, each having the smaller amplitude, which swingbetween 0 V (ground level) and VINTL. The VINTL is a small voltage ofthe order of 0.6 V. Consequently, if the potential of the second groundline 57 is raised only slightly, a malfunction may occur in the drivercircuit 6a of the second circuit block 52. According to the presentembodiment, however, it has become possible to effectively prevent thepower-source noise resulting from the operating current in the firstcircuit block 51 from intruding into the second circuit block 52, sothat the malfunction of the driver circuit 6a in the second circuitblock 2 can be prevented.

Preferably, the threshold voltage of the Qn72 serving as a MOS diode isminimized to 0 V or less.

FIG. 10 is a circuit diagram showing the internal structure of thesource voltage reducing circuit 80 shown in FIG. 9. The source voltagereducing circuit 80 is for generating the VINTL from the VINT which wasgenerated from the VCC by another source voltage reducing circuit (notshown). The source voltage reducing circuit 80 comprises: a controlterminal 81 for accepting a control clock; an output terminal 82 foroutputting the VINTL; a resistor 83; first to third PMOS transistorsQp81 to Qp83; and first to fourth NMOS transistors Qn81 to Qn84.

The resistor 83 and Qn81, which are connected in series to each other,constitute a reference potential generating circuit 84 for generating apotential VREF to be used as a reference for the VINTL. The referencepotential generating circuit 84 utilizes the threshold voltage of theQn81. As shown in FIG. 9, at least the ground potential of the referencepotential generating circuit 84 is obtained through the second groundline 57.

The Qp81, Qp82, and Qn82 to Qn84 constitute a comparing circuit 85 forcomparing the VINTL with the VREF. The Qp81 and Qp82 are connected tothe VINT so as to constitute a power source of parallel-current-mirrortype. The Qn82 and Qn83 are connected on the ground side of the powersource constituted by the Qp81 and Qp82. To the gate of the Qn82 isapplied the VREF and to the gate of the Qn83 is feedbacked the VINTL, sothat the Qn82 and Qn83 constitute a differential amplifier. The sourcesof the Qn82 and Qn83 are connected to the ground line via the Qn84serving as a common switching element which has its gate connected tothe control terminal 81. The threshold voltages of the Qn82 and Qn83 areset to low values (0 V to 0.3 V) so as to enhance the driving forces ofthe Qn82 and Qn83, similarly to the Qn11 and Qn13 in the above drivercircuit.

The Qp83 constitutes an output circuit 86 for outputting the VINTL tothe output terminal 82 and is designed so that the potential at theconnection between the Qp81 and Qn82 is applied to its gate.

With the structure shown in FIGS. 9 and 10, even if the potential of thesecond ground line 57 should vary, the output VREF of the referencepotential generating circuit 84 varies in response to the potentialvariation, so that the voltage between the output terminal 82 of thesource voltage reducing circuit 80 and the second ground line 57 ismaintained at a fixed value VINTL, thereby preventing the malfunction ofthe driver circuit in the second circuit block 52. Moreover, since thethreshold voltages of the Qn82 and Qn83 in the comparing circuit 85 areset to low values so as to enhance the driving forces of the Qn82 andQn83, even when the levels of the VREF and VINTL are low, a properoperation is ensured for the comparing circuit 85 as well as anexcellent performance is ensured for the source voltage reducing circuit80.

Although the VINTL was generated from the VINT in the structure of FIG.10, it is possible to generate the VINTL directly from the VCC.

Second Embodiment

Below, a second embodiment of the present invention will be describedwith reference to the drawings.

FIG. 11 is a circuit diagram partially showing a data transmissioncircuit in a DRAM according to the second embodiment. The datatransmission circuit of the second embodiment was obtained by furtherproviding an equalizing circuit 60 between the driver circuit 6a andpair of data lines 20 in the data transmission circuit of the DRAMaccording to the first embodiment.

In FIG. 11, the internal structure of the driver circuit 6a is the sameas that of the first embodiment (see FIG. 6). However, a first controlsignal CONT1a to be applied to the control terminal 13 in the presentembodiment is different from the CONT1 used in the first embodiment inthat the CONT1a is maintained at the HIGH level only in the former halfof each data transmission cycle.

The equalizing circuit 60 is for equalizing the potentials of the pairof data lines 20. The equalizing circuit 60 comprises: a pair ofdifferential input terminals 61 and 62 connected to the differentialoutput terminals 14 and 15 of the driver circuit 6a; a control terminal63 for accepting an equalize control signal EQ; a pair of differentialoutput terminals 64 and 65 connected to the pair of data lines 20; andan NMOS transistor Qn61. The Qn61 is interposed between the differentialoutput terminals 64 and 65 so as to equalize the potentials of the pairof data lines 20 and is designed so that the EQ is applied to its gate.

Although an amplifying circuit and a latch circuit, which are the sameas those used in the first embodiment, are connected in the lower stageof the pair of data lines 20, thereby constituting the whole datatransmission circuit of the present embodiment, the drawing of theamplifying and latch circuits is omitted here.

FIGS. 12(a) to 12(h) are timing charts showing the operation of the datatransmission circuit of the present embodiment. In the former half ofeach data transmission cycle, the CONT1a and CONT3 are raised to theHIGH levels so that the IN/XIN having the amplitude VINT are convertedby the driver circuit 6a to the OUT/XOUT having the smaller amplitudeVINTL, which are then amplified by the amplifying circuit 30 to theAOT/XAOT having the amplitude VINT. The resulting AOT/XAOT are thenlatched by the latch circuit 40, thereby determining the BOT/XBOT. Afterthe BOT/XBOT were thus determined, i.e., in the latter half of the datatransmission cycle, the CONT 2 and EQ are raised to the HIGH levels.Consequently, the operation of the amplifying circuit 30 is halted insynchronization with the latching of the AOT/XAOT by the latch circuit40, while the potentials OUT/XOUT of the pair of data lines 20 areequalized by the Qn61 of the equalizing circuit 60.

According to the present embodiment, the time required for a potentialdifference between the pair of data lines 20 to reach a specified valueis reduced due to the equalization of the pair of data lines 20, whichimplements data transmission at a higher speed. Moreover, since theequalizing operation is performed in the latter half of the datatransmission cycle, the access speed is free from an adverse effect.

Although the NMOS transistor Qn61 for equalization is interposed betweenthe differential output terminals 14 and 15 of the driver circuit 6a andthe pair of data lines 20 in the present embodiment, the transistor canbe disposed anywhere provided that it can equalize the potentials of thepair of data lines 20.

Below, a description will be given to a performance comparison between aconventional data transmission circuit in a DRAM and the datatransmission circuits according to the above first and secondembodiments.

FIG. 13(a) shows a simulation circuit (DT) of a driver circuit composedof CMOS transistors in the conventional data transmission circuit. Thetwo control signals CONT/XCONT in FIG. 13(a) are complementary to eachother. FIG. 13(b) shows a simulation circuit (SHT1) corresponding to thedriver circuit composed of NMOS transistors in the data transmissioncircuit according to the above first embodiment. FIG. 13(c) shows asimulation circuit (SHT2) corresponding to the driver circuit providedwith the equalizing circuit in the data transmission circuit accordingto the second embodiment.

FIGS. 14(a) to 14(d) are timing charts showing conditions for asimulation using the DT, SHT1 and SHT2. In the present simulation,16-bit data was transmitted in a cycle time t_(C) of 20 ns under theconditions of: VINSTL=0.6 V; RL=1.8 kΩ; and CL=4.5 pF.

FIG. 15 is a view showing the results of a simulation on the powerconsumption of the DT, SHT1, and SHT2. At VINT=2.5 V, the powerconsumption of the SHT1 is less than the power consumption of the DT by15 mA. The power consumption of the SHT2 is far less than the powerconsumption of the SHT2.

FIG. 16 is a view showing the results of a simulation on the delay timeof the DT, SHT1, and SHT2. The drawing shows delay time t_(D) in each ofthe DT, SHT1, and SHT2 for comparison. In the DT, the delay time t_(D)is the time that has elapsed since the CONT/XCONT reached half thepotential of the VINT till a potential difference of 0.1 V appeared asthe OUT/XOUT. In the SHT1, delay time t_(D) is the time that has elapsedsince the CONT1a reached half the potential of the VINT till a potentialdifference of 0.1 V appeared as the OUT/XOUT. In the SHT2, the delaytime t_(D) is the time that has elapsed since the CONT1a reached halfthe potential of the VINT till a potential difference of 0.1 V appearedas the OUT/XOUT. It will be appreciated from the drawing that the SHT1achieves higher-speed data transmission than the DH and the SHT2achieves higher-speed data transmission than the SH1.

Third Embodiment

Below, a third embodiment of the present invention will be describedwith reference to the drawings.

FIG. 17 is a circuit diagram of an amplifying circuit 30a for use in adata transmission circuit of a DRAM according to a third embodiment. Thedata transmission circuit according to the third embodiment was obtainedby replacing the amplifying circuit 30 in the data transmission circuitof the DRAM according to the first embodiment with the amplifyingcircuit 30a. In the upper stage of the amplifying circuit 30a of FIG. 17are connected a driver circuit and a pair of data lines, similarly tothe case shown in the first embodiment. In the lower stage of theamplifying circuit 30a is connected a latch circuit which is the same asthat used in the first embodiment, so as to constitute the whole datatransmission circuit. It is possible to interpose an equalizing circuitbetween the driver circuit and the pair of data lines, similarly to thecase shown in the second embodiment.

The structure of the amplifying circuit 30a of FIG. 17 was obtained byadding a power source controller 37 to an amplifier 36, which has thesame structure as that of the amplifying circuit 30 of the firstembodiment (see FIG. 6).

The power source controller 37 is that part of the circuit whichcontrols power supply to the amplifier 36 based on outputs from thedifferential output terminals 34 and 35. The power source controller 37comprises first and second PMOS transistors Qp37 and Qp38, which areconnected in series to each other. The Qp37 and Qp38 are interposedbetween the Qp36 for controlling power supply to the posterior part ofthe amplifier 36 and the VINT. The Qp37 has its gate connected to theterminal 35, which is one of the pair of differential output terminals34 and 35. The Qp38 has its gate connected to the other differentialoutput terminal 34.

The turning on and off of the Qp37 and Qp38 constituting the powersource controller 37 is controlled based on the pair of differentialsignals, each having the amplitude VINT, at the pair of differentialoutput terminals 34 and 35, which has been amplified by the amplifier36. After an output of the amplifying circuit 30a and an output of thelatch circuit in its lower stage were determined, when the CONT2 on theHIGH level is inputted to the control terminal 33 so as to halt theoperation of the amplifying circuit 30a, either of the differentialoutput terminals 34 and 35 reaches a potential substantially equal tothe VINT, so that either of the Qp37 and Qp38 is inevitably turned off.Consequently, the current flowing through the Qp36 can be cut offcompletely, so that the operation of the amplifier 36 is surely halted.While the amplifier 36 is operating, each of the Qp37 and Qp38 is turnedon due to the equalization of the potentials of the differential outputterminals 34 and 35.

The amplifying circuit 30a of the present embodiment is effective inreducing power consumption even in the case where the turning off of theQp36 is delayed, since the amplifying circuit 30a is automaticallyhalted if outputs from the differential output terminals 34 and 35 aredetermined to a certain extent.

In the present embodiment, a PMOS transistor for feedback, which issimilar to the Qp37 and Qp38, is not interposed between the Qp35 forcontrolling power supply to the anterior part of the amplifier 36 andthe VINT for fear that the amplifier 36 cannot follow a potential changeat the differential input terminals 31 and 32. These measures have beentaken in consideration of the case where a faulty signal (faulty data)is temporarily inputted to the differential input terminals 31 and 32.Since the load on the anterior part of the amplifier 36 is small, acurrent flowing through the Qp35 is negligible. However, in the casewhere it is guaranteed that input data does not vary, the PMOStransistor for feedback is preferably interposed between the Qp35 andVINT.

Thus far, the DRAM serving as an example of the LSI comprising the datatransmission circuit has been described. However, the present inventionis not limited thereto. It is applicable to a given LSI comprising adata transmission circuit. It is also applicable to data transmissionbetween a plurality of chips.

We claim:
 1. A data transmission circuit for use in a semiconductorintegrated circuit comprising:a first circuit for converting a firstpair of differential signals, each having a first amplitude, to a secondpair of differential signals, each having a second amplitude smallerthan said first amplitude; a pair of signal lines for transmitting thesecond pair of differential signals obtained through the conversion bysaid first circuit; a second circuit for converting the second pair ofdifferential signals transmitted through said pair of signal lines to athird pair of differential signals, each having a third amplitude, saidsecond circuit having,a pair of differential input terminals foraccepting said pair of differential signals; an amplifier for amplifyingthe pair of differential signals inputted via said pair of differentialinput terminals; a pair of differential output terminals for outputtingthe pair of differential signals which have been amplified by saidamplifier; and a power source controller for controlling power supply tosaid amplifier based on outputs from said pair of differential outputterminals; and a third circuit for latching the third pair ofdifferential signals obtained through the conversion by said secondcircuit.
 2. A data transmission circuit for use in a semiconductorintegrated circuit comprising:a first circuit for converting a firstpair of differential signals, each having a first amplitude, to a secondpair of differential signals, each having a second amplitude smallerthan said first amplitude; a pair of signal lines for transmitting thesecond pair of differential signals obtained through the conversion bysaid first circuit; a second circuit for converting the second pair ofdifferential signals transmitted through said pair of signal lines to athird pair of differential signals, each having a third amplitude; and athird circuit for latching the third pair of differential signalsobtained through the conversion by said second circuit, wherein saidfirst pair of differential signals are logic signals, each having a highlevel and a low level, and the high level of each of said logic signalsis equal to a first reduced voltage having been generated inside saidsemiconductor integrated circuit based on a source voltage supplied fromthe outside of said semiconductor integrated circuit.
 3. A datatransmission circuit for use in a semiconductor integrated circuitcomprising:a first circuit for converting a first pair of differentialsignals, each having a first amplitude, to a second pair of differentialsignals, each having a second amplitude smaller than said firstamplitude; a pair of signal lines for transmitting the second pair ofdifferential signals obtained through the conversion by said firstcircuit; a second circuit for converting the second pair of differentialsignals transmitted through said pair of signal lines to a third pair ofdifferential signals, each having a third amplitude; and a third circuitfor latching the third pair of differential signals obtained through theconversion by said second circuit, wherein said second pair ofdifferential signals are logic signals, each having a high level and alow level, and the high level of each of said logic signals is equal toa second reduced voltage having been generated inside said semiconductorintegrated circuit based on a source voltage supplied from the outsideof said semiconductor integrated circuit.
 4. A data transmission circuitfor use in a semiconductor integrated circuit comprising:a first circuitfor converting a first pair of differential signals, each having a firstamplitude, to a second pair of differential signals, each having asecond amplitude smaller than said first amplitude; a pair of signallines for transmitting the second pair of differential signals obtainedthrough the conversion by said first circuit; a second circuit forconverting the second pair of differential signals transmitted throughsaid pair of signal lines to a third pair of differential signals, eachhaving a third amplitude; and a third circuit for latching the thirdpair of differential signals obtained through the conversion by saidsecond circuit, wherein a ground line of said first circuit is providedindependently of ground lines of other circuits in said semiconductorintegrated circuit.
 5. A data transmission circuit for use in asemiconductor integrated circuit comprising:a first circuit forconverting a first pair of differential signals, each having a firstamplitude, to a second pair of differential signals, each having asecond amplitude smaller than said first amplitude; a pair of signallines for transmitting the second pair of differential signals obtainedthrough the conversion by said first circuit; a second circuit forconverting the second pair of differential signals transmitted throughsaid pair of signal lines to a third pair of differential signals, eachhaving a third amplitude; and a third circuit for latching the thirdpair of differential signals obtained through the conversion by saidsecond circuit; wherein the operation of said second circuit is haltedin synchronization with the latching of said third pair of differentialsignals by said third circuit.
 6. A data transmission circuit for use ina semiconductor integrated circuit comprising:a first circuit forconverting a first pair of differential signals, each having a firstamplitude, to a second pair of differential signals, each having asecond amplitude smaller than said first amplitude; a pair of signallines for transmitting the second pair of differential signals obtainedthrough the conversion by said first circuit; a second circuit forconverting the second pair of differential signals transmitted throughsaid pair of signal lines to a third pair of differential signals, eachhaving a third amplitude; a third circuit for latching the third pair ofdifferential signals obtained through the conversion by said secondcircuit; and a fourth circuit for equalizing the potentials of said pairof signal lines.
 7. A data transmission circuit according to claim 6,wherein,in the former half of a data transmission cycle, said first andsecond circuits are operated so as to obtain said third pair ofdifferential signals from said first pair of differential signals and,in the latter half of said data transmission cycle, the operation ofsaid second circuit is halted in synchronization with the latching ofsaid third pair of differential signals by said third circuit and saidfourth circuit is operated so as to equalize the potentials of said pairof signal lines.